Flowmeter

ABSTRACT

An electromagnetic flow meter is configured as an insert for insertion into an in-situ housing connected in a flow line. This can enable a body previously installed for use with an insert of a mechanical flow meter to be adapted for use with an insert of an electromagnetic flow meter without having to disconnect the body from a mains supply.

The present invention relates to non-mechanical flow meters, in apreferred embodiment to an electromagnetic flow meter, in particular toa flow meter primarily, but not exclusively, designed for commercial andnetwork monitoring applications, and a method of installing the same.

Bulk flow meters monitor large flows of water for water systemsmanagement and commercial billing purposes. An example of a bulk flowmeter is our H4000 (HELIX® 4000) Woltmann-type meter in which a rotorrotates in a measuring chamber receiving a flow of water from the mainssupply and a revolution counter counts the number of revolutions of therotor to provide a measurement of the volume of water passing throughthe meter. The H4000 meter is interposed between flanged upstream anddownstream portions of a supply pipe so that the flow of water in thepipe flows directly through the meter. Such flow meters are typicallyreferred to as “throughflow” meters. To facilitate maintenance, themeasuring mechanism, including the rotor, measuring chamber andregister, is removable from a body having flanged ends connected to themains supply to enable a new pre-calibrated mechanism of the same typeto be easily and quickly installed in the body.

Such “mechanical” flow meters are subject to wear of the moving part orparts of the meter. Any wear tends to cause the accuracy of themeasurement of the amount of water passing through the meter todeteriorate. Mechanical flow meters are also prone to damage bysuspended solids. As a result, the service life of such meters can berelatively short.

Electromagnetic meters do not suffer the problems of mechanical wear.However, one problem with known electromagnetic flowmeters is that theytend to be bulky devices, requiring substantial structures such as fieldgenerating coils and measurement apparatus attached to the exterior ofthe conduit in which the flow is to be measured. This can limit theapplicability of electromagnetic flow meters in applications where spaceis at a premium, for lower flow rates. In addition, maintenance of theflow meters can be a major undertaking, requiring removal of asubstantial section of pipe work with associated coils and meterequipment. Furthermore, generating a uniform magnetic field across asubstantial conduit may require large amounts of power and may bedifficult to achieve.

In at least its preferred embodiments the present invention seeks tosolve these and other problems.

In a first aspect the present invention provides an electromagnetic flowmeter configured as an insert for insertion into an in-situ housingconnected in a flow line.

An electromagnetic flow meter operates by developing a magnetic fieldacross a measurement duct, and detecting a voltage induced in waterflowing in the duct the magnitude of the induced voltage being relatedto the velocity of the water flowing in the duct As the meter has nomoving parts and is unaffected by suspended solids, its service lifecould be in excess of 20 years. Electromagnetic flow meters also tend tohave a greater measuring range than mechanical flow meters. Such anelectromagnetic flow meter Is described in our International patentapplication no WO 98/49528, the contents of which are incorporatedherein by reference.

Replacement of mechanical through-flow meters with electromagneticthrough-flow meters of the type described in WO98/49528 has not hithertobeen contemplated, since it could be a time consuming, and thus costlyexercise to remove the entire mechanical throughflow meter, includingthe flanged body connected to the mains supply, and install the newelectromagnetic flow meter.

By configuring the electromagnetic flow meter as an insert for a housingalready connected to a mains supply, this can enable an insert for amechanical meter to be easily and quickly replaced to transform themeter into a more accurate and longer lasting electromagnetic flowmeter.

The insert preferably comprises a flow measurement duct means forgenerating a magnetic field across the duct, and means for deriving ameasurement of the rate of flow of fluid through the duct from thevoltage induced by the magnetic field in fluid flowing through the duct.

In one preferred embodiment the insert comprises means for divertingpart of the flow of fluid away from the duct. This can enable the amountof fluid flowing through the duct to be restricted to an amount withinthe measuring range of the meter, with the bulk of the fluid beingdiverted away from the duct. Preferably, the diverting means comprisesat least one channel. The or each channel preferably extends about theduct. This can aid in minimizing the size of the or each insert so as tofit inside the housing.

Preferably, said one insert is shaped to provide said at least onechannel. This can enable the duct generating means, deriving means andsaid at least one channel to be provided by a single insert.

Preferably, the or each channel is defined at least in part by theexternal surface of the insert. This can simplify the manufacture of theinsert. Preferably, the insert is shaped to provide a pair of saidchannels extending about respective sides thereof. The or each channelpreferably comprises a convergent inlet portion and a divergent outletportion. As the duct typically has a convergent inlet portion and adivergent outlet portion, in order primarily to reduce the spacingbetween electrodes for detecting the voltage induced in fluid flowingthrough the duct, it is advantageous to shape each channel in a similarmanner. This can assist in maintaining the flow of fluid through eachchannel at a rate which is proportional to the rate of flow of fluidthrough the duct, so that the flow measurement is proportional to therate of flow of fluid through the meter, and can also enable the flow offluid leaving the duct to recombine with the flow of fluid from eachchannel with minimum turbulence before flowing from the housing.

In another preferred embodiment, the meter comprises an additionalinsert for channelling the flow of fluid into the duct. This can enablethe mouth of the duct to have a different shape to that of the inlet.The additional insert preferably comprises a sleeve having a convergentcross-section in order to channel the flow of fluid into the duct.

The present invention extends to an electromagnetic flow meter asaforementioned, comprising a housing connected to a flow line, theinsert being inserted in said housing.

The housing preferably has an inlet substantially co-axial with anoutlet thereof. The duct is preferably co-axial with the inlet andoutlet.

The present invention also provides a method of installing anelectromagnetic flow meter as aforementioned, comprising replacing acartridge installed in a housing connected in a flow line with saidinsert or inserts

In a further aspect the invention provides a cartridge insertable into aflow conduit, the cartridge having a through bore defining a flowpassage, and metering means for measuring flow of fluid in the throughbore.

In a preferred application, the meter is an electromagnetic flowmeterand the metering means comprises field generating means for generating amagnetic field across a fluid passing through the through bore; andsensing electrodes for sensing a potential developed in a fluid passingthrough the through bore.

In this way, rather Fan building a bulky flow meter around a conduit orhaving to replace a section of conduit with a flow meter, anelectromagnetic flow meter cartridge can simply be inserted into theconduit without substantially increasing the dimensions of the conduit.Furthermore, because the through bore has smaller dimensions than theconduit, the flow velocity through the flow meter is greater than thatin the conduit which can lead to improved measurement accuracy.

The cartridge is preferably provided in a fluid-proof housing.

The housing may have dimensions to occupy a conduit of predeterminedstandard dimensions. For example, the exterior dimensions of the housingmay be arranged to fit within a standard circular or rectangular sectionconduit in which an insertion hole has been bored.

More preferably, the conduit is arranged to be inserted into a conduitinsertion housing comprising first and second coupling portions forcoupling with respective upstream and downstream flow conduits and ameter insertion orifice into which a cartridge containing a flow metercan be inserted.

In a further aspect the invention provides a flow metering kitcomprising:

a conduit insertion housing comprising first and second couplingportions for coupling with respective upstream and downstream flowconduits and a meter insertion orifice into which a cartridge containinga flow meter can be inserted: and

an insertable cartridge having a through bore defining a flow passage,and metering means for measuring flow of fluid in the through bore.

A preferred application is an electromagnetic flow meter. However, thecartridge assembly may be used to contain other flow metering equipment,such as a mechanical flow meter or an ultrasound or other flow meter.

In a further aspect, the invention provides a method of installing aflow meter in a conduit, the method comprising

installing a housing in the conduit, the housing having an openingarranged to receive a cartridge containing a flowmeter; and

installing a cartridge containing a flowmeter in the housing.

In a related aspect the invention provides a flowmeter for measuring theflow of fluid in a conduit, the flowmeter comprising:

a metering body comprising a housing containing a non-mechanicalflowmeter arranged to measure the flow of fluid around the meteringbody; and

mounting means for mounting the metering body in the path of fluid.

According to a preferred embodiment the invention provides a flowmeterfor measuring the flow of fluid in a conduit the flowmeter comprising:

a metering body comprising a housing containing field generating meansand potential sensing electrodes; and

mounting means for mounting the metering body in the path of fluid.

Thus, by mounting the metering assembly inside the conduit In an“inside-out” arrangement, the dimensions of the flowmeter can be greatlyreduced.

Preferably,the metering body is streamlined and preferably also themetering body is fluid-tight, in a preferred arrangement, the meteringbody is elongate, and the mounting means is arranged so that the axis ofelongation is substantially parallel to the path of fluid flow.

Preferably, the dimensions of the metering body are chosen such that thefluid flow is either substantially undisturbed by the presence of themetering body, or such that the metering body defines the fluid flow. Inmost cases this means that the cross sectional surface of the meteringbody should either be substantially smaller than the conduit in whichthe metering body is to be mounted, or large enough (i.e. not muchsmaller than the internal section of the conduit) so that the fluid flowis defined by the (e.g. annular) gap between the internal surface of theconduit and the external surface of the metering body. The flow will notbe strictly laminar, but it is preferred that the metering body isformed such that the flow is substantially laminar, at least in thevicinity of the metering body, so as to enable reliable measurements tobe taken.

Advantageously, in one embodiment, the mounting means comprises a flangearranged to be clamped between adjacent flanges of conduit sections in apipeline. This provides a particularly compact and readily insertablearrangement.

Preferably, the metering body is centrally mounted within the conduit.

In a particularly preferred implementation, the mounting assemblycomprises a flange having means for axially aligning the metering bodywith the conduit. Preferably, the alignment means comprises at least oneprojection, preferably a plurality of projections arranged to engagewith clamping bolts on rotation of the flange relative to the bobs.Thus, the exterior of the flange preferably comprises a series ofpartial spiral sections, the number of spiral sections corresponding tothe number of clamping bolts, for example 4, preferably at least 3, theminimum diameter being less than the diameter between the bolts and themaximum diameter being greater than the diameter between the bolts sothat a position exists which the exterior of the flange rests againstthe bolts. In the case of a flange for a larger diameter conduit, whichmay have a large number of bolts, projections may be provided to engagewith only a proportion of the bolts. Between the bolt-engagingprojections, the exterior should preferably have a generally circularsection.

In a method aspect, the invention provides a method of installing aflowmeter in a pipeline, the method comprising:

providing adjacent separated portions of a pipeline and clamping amounting flange to which is mounted an internal flowmeter between theadjacent sections of the flange.

As an alternative mounting arrangement, the flowmeter may be mounted ina cartridge. The cartridge can be inserted directly into the conduit orinto a housing designed to take the conduit and connected with theremainder of the pipeline.

Preferred features of the present invention will now be described, byway of example only, with reference to the accompanying drawings inwhich:

FIG. 1 is a perspective view of an in-line mechanical flow meter;

FIGS. 2 to 5 are perspective views illustrating steps in theinstallation of a first embodiment of an electromagnetic flow meter,

FIG. 6 illustrates a second embodiment of an electromagnetic flow meter;

FIG. 7 is a perspective view of a third embodiment;

FIG. 8 is a perspective view showing detail of the self-centringclamping flange;

FIG. 9 is a plan view of the third embodiment;

FIG. 10 is sectional view of the third embodiment; and

FIG. 11 is a schematic perspective view of an insertable cartridge inaccordance with a fourth embodiment of the invention;

FIG. 12 is a front view of the embodiment of FIG. 11;

FIG. 13 is a section through B—B of FIG. 12; and

FIG. 14 is a section through C—C of FIG. 12;

FIG. 15 is an exploded view showing internal detail of the metering bodyof the third and fourth embodiments;

FIG. 16 is a schematic perspective view of an insertable cartridge inaccordance with the fifth embodiment of the invention;

FIG. 17 is a schematic view of the embodiment of FIG. 16 showinginterior details;

FIG. 18 shows a section through A—A of FIG. 17 showing interior details;

FIG. 19 is a section through B—B of FIG. 17 illustrating tapering of thethrough bore upstream and downstream of the measuring location;

FIG. 20 shows a perspective view of an insertable cartridge according toa further embodiment;

FIG. 21 shows a side view (in section) of the cartridge of FIG. 20; and

FIG. 22 shows a section through A—A of FIG. 21.

FIG. 1 is a perspective view of an example of a mechanical in-line flowmeter. The example is shown in FIG. 1 is our H4000 (HELIX®4000)Woltmann-type meter in which a rotor is rotated inside a measuringchamber by a flow of water received from the mains supply and the numberof revolutions of the rotor is counted to provide a measurement of thevolume of water flowing in the mains supply.

The meter includes a body 10 having co-axial flanged end portions 12, 14for connection in a mains supply pipe between flanged ends of respectivepipe sections. As shown more clearly in FIG. 2, as is typical ofmechanical flow meters the measuring mechanism, which includes, interalia, the rotor, measuring chamber, revolution counter and register, ishoused inside an insert 16 insertable into the body 10 of the meter.This enables the insert 16 to be replaced by a new pre-calibrated insertat the end of the service lifetime of the meter without having todisconnect the body 10 from the mains supply.

The installation of an electromagnetic flow meter according to a firstembodiment of the present invention will now be described with referenceto FIGS. 2 to 5.

First, with reference again to FIG. 2, insert 16 is removed from thebody 10 of the mechanical flow meter. Referring now to FIG. 3, in thisfirst embodiment the insert 14 is replaced by three inserts 18, 20 and22 of an electromagnetic flow meter. Insert 18 comprises a flowmeasurement duct 24. The duct 24 comprises a non-magnetic,non-conducting, non-permeable tube eg of a plastics material treated torender it impervious to water seepage under pressure. The tube has asubstantially rectangular cross-section at its inlet 26 and outlet 28ends blended by contraction (converging) and diffusion (diverging)portions to an intermediate portion of rectangular cross-section throughwhich the rate of flow of fluid through the meter is determined. Theduct 24 is shaped to achieve a uniform flow profile through theintermediate portion for a range of fluid flow rates in the duct withminimum variation in the pressure of the fluid leaving the duct at theoutlet. A pair of electrode housings are provided in the duct, oneelectrode being disposed in each electrode housing so that theelectrodes are disposed orthogonally across the direction of flow offluid in said flow tube and orthogonal also to magnetic field.

Insert 18 also comprises means for generating a magnetic field acrossthe duct. In this embodiment the generating means comprises first andsecond pole pieces for directing an alternating magnetic field acrossthe measurement duct. Each pole piece is surrounded by an excitationcoil 30 for generating the magnetic field in the pole pieces, with areturn path 32 for the magnetic flux being provided between the upperand lower pole pieces

Insert 18 further comprises means for deriving a measurement of the rateof flow of fluid through the duct from the voltage induced by themagnetic field in the fluid flowing through the duct. This is providedinside casing 40 of the inlet 18, and comprises circuitry forcalculating the flow rate from the voltage detected by the electrodeswhich is induced in the fluid by the magnetic detail. Further details ofthis circuitry is contained in our aforementioned Internationalapplication no WO98/49528. The casing 40 may include a display.

As shown in FIG. 3, the bore of the duct 24 has a different shape thanthat of the inlet 42 of the flanged end portion 12 of the body 10. Inorder to channel fluid flowing from the inlet 42 into the duct 24,insert 20 in the form of a convergent sleeve is inserted into the inlet42 in order to channel fluid flowing from the inlet into the duct. Asimilar insert 22 in the form of a divergent sleeve is inserted into theoutlet of flanged portion 14 in order to channel fluid flowing from theduct to the outlet.

To install the electromagnetic flow meter, as shown In FIG. 4 first thesleeves 20 20 and 22 are inserted into the inlet and outlet respectivelyof the flanged portions 12, 14 of the body 10. Insert 18 is theninserted into the body so that the duct 2415 is co-axial with the inletand outlet, the resultant electromagnetic flow meter being shown in FIG.5. The measurement of the rate of flow of fluid through the duct 24 isproportional to the rate of flow of fluid in the mains supply, and sothe circuitry of the meter can be calibrated so that the displayindicates the volume of fluid passing through the meter.

FIG. 6 illustrates a second embodiment of an electromagnetic flow meteraccording to the present invention. The second embodiment is similar tothe first embodiment, in that an insert 50 comprising a flow measurementduct 24, generating means, deriving means and a display 52 is insertedinto the body 10. However, in this second embodiment the insert is inthe form of a cartridge 50 housing the flow measurement duct, generatingmeans and deriving means. To minimise costs, the working parts of anelectromagnetic flow meter intended for domestic metering applicationsmay form the basis of the cartridge 50. In this embodiment, the externalsurface of the cartridge 50 is shaped to define, with the internalsurface of the body 10, channels 60 extending about the duct 24, so thatonly part of the flow of fluid from the inlet 42 enters the duct and theremainder of the flow of fluid is diverted away from the duct andtowards the outlet in flanged portion 14. As shown in FIG. 6, eachchannel 60 comprises a convergent inlet portion and a divergent outletportion. In operation, most of the flow of fluid entering the meter isdiverted away from the duct 24 by the channels 60, so that the amount offluid entering the measurement duct is within the normal measuring rangeof the meter. As the duct has a convergent and divergent portions, inorder primarily to reduce the spacing between electrodes for detectingthe voltage induced in fluid flowing through the duct, it isadvantageous to shape each channel 60 in a similar manner. This canassist in maintaining the flow of fluid through each channel at a ratewhich is proportional to the rate of flow of fluid through the duct 24,so that the flow measurement is proportional to the rate of flow offluid through the meter, and can also enable the flow of fluid leavingthe duct 24 to recombine with the flow of fluid from each channel 60with minimum turbulence before flowing from the outlet of the body 10.As in the first embodiment, the circuitry of the meter can be calibratedso that the display indicates the volume of fluid passing through themeter.

As described above, the present invention enables a mechanical flowmeter to be easily and quickly replaced by an electromagnetic flowmeter. In comparison to a mechanical flow meter, an electromagnetic flowmeter is not subject to wear and is unaffected by suspended solids, andthus has a greater service lifetime. Another advantage of the presentinvention is that there is no need to replace the body 10 in order toinstall the electromagnetic flow meter. Accordingly, installation of theelectromagnetic flow meter is facilitated, as there is no need todisconnect the body from the mains supply. In addition, the initialinvestment in the body 10 of the mechanical meter and its installationis maintained, as the body 10 is not discarded.

In the above, reference has been made to a H4000 mechanical meter.However, it will be appreciated that the invention is not limited toreplacement of only this particular type of meter by an electromagneticflow meter, but is applicable for use in replacing all types ofmechanical meter in which the measuring mechanism is inserted orotherwise located in a body.

To summarize the above, an electromagnetic flow meter is configured asan insert for insertion into an in-situ housing connected in a flowline. This can enable a body previously installed for use with an insertof a mechanical flow meter to be adapted for use with an insert of anelectromagnetic flow meter without having to disconnect the body from amains supply.

Referring now to FIGS. 7 to 10, a third embodiment will now bedescribed. A metering body 140 contains field generating coils andsensing electrodes (not shown). This is suspended within the bore 120 ofa mounting member 122 comprising a flange by means of 3 symmetricallydisposed struts 126. The flange has four protrusions 128 a, 128 b, 128c, 128 d which extend in a generally spiral fashion from a relativelysmall radius over a relatively large radius whereby, on rotation of theflange, a portion of the projections can be brought into contact withmounting bolts.

The wiring for the field generating coil and the sensing electrodes iscarried to the exterior through a passage in one or more of the mountingstruts 126 and is connected to a conventional flowmeter controlapparatus.

Referring to FIGS. 11 to 14, a fourth embodiment is shown.

In the fourth embodiment, a similar “inside-out” flowmeter is used.However, the mounting assembly for this comprises a cartridge 101′which, in this embodiment, is formed of an upstream housing 101 a and adownstream housing 101 b. This defines a through bore 144, having aninlet 130 and an outlet 132. A flowmeter metering body 140 is suspendedwithin through bore. A sealing ring, not shown, may be mounted betweenthe two housing portions. The flowmeter metering body contains fieldgenerating means within the flowmeter metering body 140 and haspotential sensing electrodes on the exterior of the flowmeter meteringbody 140. Thus, the flow velocity sensed is that of the fluid flowing inthe annular space between the flowmeter body 140 and the interior of thehousing 101′.

Referring to FIG. 15, the internal structure of the metering body 140will be explained. The same or similar structure may be employed withthe mounting means of either embodiment or other mounting structures.The metering body 140 has two electrodes 202 (only one of which isshown) on opposite sides of the body for sensing the potential developedacross the fluid. A further electrode 204, mounted centrally (here atthe upstream end of the body) is provided as an earthing electrode orearth reference electrode. This is particularly useful in providing anearth reference when the mounting means does not earth the fluid (forexample in the case of a cartridge made of plastics material; aparticularly advantageous construction comprises a plastics meteringbody and an earthing electrode mounted substantially centrally withinthe fluid). An iron circuit 206 is provided defining coil spaces 208 inwhich field generating coils are wound (for sake of clarity, the coilsthemselves are not shown in FIG. 15).

It will be appreciated that modifications of detail may be made. Inparticular, the mounting arrangements may be varied to suit a variety ofconduits, the important principle being that the flowmeter is mountedwithin a conduit and that the fluid flows around rather than through theflowmeter. For example, the metering body could even be mounted in aconventional spool of pipeline, although this of course diminishes theadvantages of having a compact metering body. Metering body dimensionsof the order of a centimetre or two in diameter are possible andconsiderable advantages are obtainable in the case of small meteringbodies. The metering body may be formed most advantageously fromplastics material. The principles may, however, be employed with muchlarger meters, for mounting in pipelines up to a metre or even more indiameter. In the latter case, a considerable saving may be made byobviating the need for a large spool in which the meter is assembled andpower requirements may also be reduced. In the case of a large boremeter in particular, the meter need not be mounted separately, but maybe mounted on a boom, in some cases movably.

A fifth embodiment will now be described.

Referring to FIGS. 16 to 19, the cartridge has a mounting flange and afluid proof housing 312. Within the fluid proof housing is an ironcircuit 320 having coils 322 a, 322 b. Also mounted within the housingand protruding to make contact with the fluid are electrodes 324. Thehousing provides a tapered inlet orifice 330 and tapered outlet orifice332 either side of metering through bore 334.

The field generating coils and electrodes are connected to the controlapparatus of a flow meter in the normal way.

In certain cases, the metering through bore may have a square sectionand may be larger. In certain applications, only a single coil may beprovided to generate the field.

A preferred embodiment is shown in FIGS. 20 to 22. These drawings show acartridge 401 similar to that illustrated in FIG. 11. The cartridge 401has a bore 402 through which the fluid may flow. A bore 404 Is providedin the cartridge (in FIG. 20 at a central position through the top wallof cartridge 401) for receiving a metering housing 406 having anelongate body. A corresponding bore or recess 408 is provided in thebottom wall of the cartridge, also for receiving the metering housing406 (FIGS. 21 and 22), so the metering body extends perpendicular to thedirection of flow through bore 402. The metering housing 406 can be ofcylindrical section, but is preferably, as shown at 410 in FIG. 20, ofstreamlined profile. The metering housing may also be cylindrical oninsertion into cartridge 401, and a wedge shaped body or similar isattached to the cylindrical metering housing 40 after insertion into thecartridge so as to form a composite structure having a streamlinedsection.

An iron circuit 412 is provided within metering housing 406. Fieldgenerating coils are located within iron circuit 412 such that amagnetic field is generated whose axis extends parallel to the meteringhousing 406. Electrodes 414 are provided for measuring a potentialdifference therebetween.

As shown in FIGS. 20 to 22, no metering duct is provided. The fluidflows around the metering body.

Each feature disclosed in the description, and/or the claims anddrawings may be provided independently or in any appropriatecombination. In particular a feature of a subsidiary claim may beincorporated in a claim for which it is not dependent

1. A non-mechanical flow meter comprising: a housing connectable in aconduit such that the housing extends across the conduit and all fluidflowing in the conduit passes through the housing; and a self-containednon-mechanical flow measurement cartridge for the measurement of flow inthe conduit, wherein the cartridge is configured for removable insertioninto the housing while the housing is in-situ in the conduit.
 2. Aflowmeter according to claim 1 wherein the flowmeter is arranged tomeasure the flow of fluid around measuring components of the cartridge;and the flowmeter comprises a mounting for mounting the measuringcomponents in the path of fluid.
 3. A flowmeter according to claim 2,wherein the cartridge contains field generating means for generating amagnetic field in the fluid around the measuring components andpotential sensing electrodes for sensing potential induced in the fluidaround the measuring components.
 4. A flowmeter according to claim 2,wherein the mounting is configured for axially aligning the cartridgewith the conduit.
 5. A flowmeter according to claim 2, wherein themounting comprises a flange arranged to be clamped between adjacentflanges of conduit section in a pipeline.
 6. A flowmeter according toclaim 4, wherein the mounting comprises at least one projection arrangedto engage with clamping bolts on rotation of the flange relative to thebolts.
 7. A flowmeter according to claim 5, wherein the mountingcomprises at least one projection arranged to engage with clamping boltson rotation of the flange relative to the bolts.
 8. A flowmeteraccording to claim 1, wherein the mounting is configured to position thecartridge on a central flow axis of the conduit.
 9. A flowmeteraccording to claim 1 wherein the cartridge is fluid-tight.
 10. Anelectromagnetic flow meter according to claim 1 wherein the cartridgecomprises a flow measurement duct, means for generating a magnetic fieldacross the duct, and means for deriving a measurement of the rate offlow of fluid through the duct from the voltage induced by the magneticfield in fluid flowing through the duct.
 11. A meter according to claim10, wherein the cartridge comprises means for diverting part of the flowof fluid through the housing away from the duct.
 12. A meter accordingto claim 11, wherein the diverting means comprises at least one channel.13. A meter according to claim 12, wherein said at least one channelextends about the duct.
 14. A meter according to claim 13, wherein theor each channel is defined at least in part by an external surface ofthe cartridge.
 15. A meter according to claim 12, wherein the or eachchannel comprises a convergent inlet portion and a divergent outletportion.
 16. A meter according to claim 15, wherein the measurement ducthas a convergent/divergent profile similar to that of the at least onechannel.
 17. A meter according to claim 10, comprising an insert forchanneling fluid into the duct.
 18. A meter according to claim 17,wherein said insert comprises a sleeve having a convergent or adivergent cross-section.
 19. A meter according to claim 1 wherein thehousing has an inlet substantially co-axial with an outlet thereof. 20.A method of installing a flow meter according to claim 1, comprisingreplacing a mechanical flowmeter cartridge installed in a housingconnected in a flow line with said cartridge.
 21. A flowmeter accordingto claim 1, wherein the cartridge is elongate and is mounted so that theaxis of elongation is substantially parallel to the direction of fluidflow.
 22. A flowmeter according to claim 1, wherein the cartridge iselongate and is mounted so that the axis of elongation is substantiallyperpendicular to the direction of fluid flow.
 23. A non-mechanical flowmeter comprising: a housing connectable in a conduit such that thehousing extends across the conduit and all fluid flowing in the conduitpasses through the housing, the housing having an aperture for insertionof a self-contained flow measuring cartridge and a seating proximate theaperture for receiving a conforming part of the cartridge; and aself-contained non-mechanical flow measurement cartridge for themeasurement of flow in the conduit, wherein the cartridge is configuredfor removable insertion into the housing via the aperture while thehousing is in-situ in the conduit by movement transversely of a flowaxis of the conduit, and comprises a part conforming in shape to theseating, and configured to be fixed thereto.
 24. A meter according toclaim 23, wherein the seating and the conforming part are flangesurfaces.
 25. A non-mechanical flow meter comprising: a housingconnectable in a conduit such that the housing extends across theconduit and all fluid flowing in the conduit passes through the housing,from an inlet thereof to an outlet thereof; a self-containednon-mechanical flow measurement cartridge for the measurement of flow inthe conduit; wherein the housing comprises inlet and outlet couplingportions for coupling with respective upstream and downstream portionsof the conduit and having respectively a flow inlet and a flow outlet;wherein the cartridge is configured for removable insertion into thehousing while the housing is in-situ in the conduit and has a measuringsection of different flow cross-section to that of the flow inlet andthe flow outlet, the meter defining a convergent flow passage from theinlet to the measuring section and a divergent flow passage from themeasuring section to the outlet.
 26. A meter according to claim 25,wherein the convergent and the divergent passages are defined byseparate inserts in the housing upstream and downstream of thecartridge.
 27. A non-mechanical flow meter comprising: a housingconnectable in a conduit such that the housing extends across theconduit and all fluid flowing in the conduit passes through the housing;and a self-contained non-mechanical flow measurement cartridge for themeasurement of flow in the conduit; wherein the cartridge is configuredfor removable insertion into the housing while the housing is in-situ inthe conduit and has a measuring section which is centrally disposed inthe flow through the housing; and wherein the housing and the cartridgedefine channels which divert part of the fluid around opposite sides ofthe measuring section and wherein the channels each have a convergentinlet portion and a divergent outlet portion.